Process of blocking ophthalmic lenses



May 23, "1933. 'HEWQ HILL PROCESS OF BLOCKING OPHTHALMIC LENSES Original Filed April 10, 1924 N mmsm 9 IW//./A v,

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M m a Patented May 23, 1933 HARE-Y 17 EILL, Q1 SOUTZ'IBRIIDGE, MASSACHUSETTS, ASSIGNOR- T AMERICAN OPTICAL GOIYILAN'Z, 0F SOUTEIBRIDGE, MASSACHUSETTS, A VQLUNTAEY ASSOCIATION 01 BEA-SSE;

PROCESS OF BLGOKING OPHTHALIEIC LENSES Division of 111 1326, Serial No. 13.2 1336.

ls invention relates to improved appa- .s 101- holding precision lenses for grmdiig, and a process for automatically centering holding such lenses during the various one ations of precision lens grinding. This application is a division of my application Serial Nun ber 705,611 filed April 10, 192%, and a continuation of my application Serial Number 11%,636 filed June 9, 1926.

The rincipal object of this invention is to provide means for automatically and precisely centering a lens blank from whicha precision lens is to be made, and to maintain the precise center thus obtained throughoutthe various manufacturing operations of grinding and finishing the lens Another object of the invention 1s to provide means to secure the lens so centered 1n that centered position to holding means that are themselves automatically centered in the various steps of production in order to maintain in such steps the precise centering obtained at the start.

Another object of the invention is to provide attaching means for such lens holding means to adapt the holding means to the various grinding and polishing operations 1 n machines used in the manufacture of precision lenses.

Still another object of the invention is to provide means for facile gauging of the thickness of the blank at fixed distances from the center thereof during the manufacturing op rations so that the blank may be ground to an exact predetermined center thickness required in precision lenses.

ilrnother object of the inventlon is to provide means toautomatically center prism, toric and irregular shaped lenses and to maintain that centering throughout the Various manufacturing operations.

Another object of the invention 1s to prov'cle local adhesive means for holding the lens blank to tne holder, hat will not become displaced durin the grinding and polishing operations of the lens.

One of the most important objects of the invention is to provide a process for precisely grinding one side of the lens blank to finished curvature, from which the lens blank may be an ication filed April 10, 1924, Serial No. 705,611. Continuation of application filed June 9,

This application filed December 28, 19. 39.

Serial No. 417,114.

automatically and precisely centered for precision grinding with localized means for securing the lens blank to holding means in such precise centered position throughout the various manufacturing operations that the first precise centering is never departed from.

l/Vith the above and other objects in View the invention consists in the novel features of construction and in the processes herein set forth and described, the preferred construction and process only being set forth by way of illustration, it being understood that modifications may be made in the construction or in the process without departing from the spirit of the invention as set forth in the accompanying claims.

Referring to the drawing,

Figure 1 is a cross section of the automatic centering device;

Figure 2 is a cross section of a modified form of centering device;

Figure 3 is a top plan view of Figure 1 Figure 4c is a cross section of a lens holding means;

Figure 5 is a top plan View of Figure 4:;

Figure 6 is a cross section of the assembled centering device and lens holding means;

Figure 7 is an end view of a grinding center attachment for the lens holder;

Figure 8 is a bottom plan view of Figure 7 Figure 9 is a cross section through the lens holder and the grinding attachment assembled; I

Figure 10 is a diagrammatic View of a grinding machine showing the assembled holder and grinding attachment in place on a grinding machine.

Referring now more particularly to the drawing, in which similar reference characters designate similar parts throughout, the numeral 1 indicates the lens blank to be ground. This blank is of optical glass of suitable refractive index for ophthalmic lenses, and has one face 2 ground and polished accurately to the desired lens curve for one face of the lens. The other face 3 of this blank is molded roughly to a standardized curve approximating closely the finished curve to which it is to be eventually ground. The

glass blank 1 is molded to a definite fixed diameter in order that the edge thickness at the extremities of its diameter may be gauged from time to time in order to determine the finished thickness of the lens at the center, which center thickness is of the utmost importance in the finished precision lens and must be accurately ascertained and worked to in order to accomplish the final prescription power of the lens.

After the face 2 of the blank 1 has been precisely finished, as described, the blank is, placed in a centering device or block 4 which has a recess 5 to receive the lens blank, and a subrecess 6 to receive the center of the lens when the lens is convex instead of concave on the side that goes down in the centering device as indicated in dotted lines in Figure 1.

In cases where toric lenses, cylindrical lenses, prismatic lenses, or lenses of other unequal configuration are to be centered, aslightly modified centering device 7, Figure 2, is utilized. This centering device has a central raised portion 8, preferably in the form of a portion of a sphere. It also has a recess 9 for receiving the lens blank. hen the blank is placed in the centering device 7 it is clear that its central portion will rest on the raised portion 8 instead of the lens blank caring on its outer extremities, as in the lens receiving device 4.

After the lens blank has been placed in the centering device 4, or 7, as the case may be, a ring lens holder 10, Figures 4, 5, 6 andv 9,

is placed upon the finished surface of the lens blank 1. The lens holder 10 is adapted to fit loosely within the centering device 4 so that it may rock to adjust itself to the curvature of th lens surface. The under side of the lens holder 10 is made in the form of a bevelled ring, as at 11, the plane of the bevelled ring being normal to the longitudinal axis of the holder 10. Owing to the bevelled ring it is, therefore, possible to get line contact throughout the extent of the ring with the finished surface of the lens blank in its centering device, where the finished surface is plano or is spherical in contour. This ring, therefore, automatically centers the lens holder to proper center upon the lens blank 1, because as is well known a circular ring will contact throughout its length with a spherical surface or with a plane surface which is of course a spherical surface with infinite radius. Where the plane of the circular ring is normal to the longitudinal axis of the lens holder the said axis will be normal to plane surface on which the ring rests and the said axis will be radial to a spherical surface on which the said ring rests, hence the lens holder when placed on the finished surface 2 of the lens will have its longitudinal axis normal to the lens surface if it is plane and radial if it is spherical, hence the finished surface 2 of the lens automatically locates the lens holder in axial grinding position on the lens. It will be noted from the drawing that the lens holder 10 is'in the form of a hollow ring, or annulus having a large central tapered recess tapering from the bottom of the ring at its widest point to the top. This tapered recess 12 is designed to permit of an adhesive being introduced into the lens holding ring and into contact with the lens blank 1. This adhesive is preferably molten pitch 13, Figure 6, which is poured into the tapered hole 12 of the lens holder and allowed to cool. Prior to inserting the pitch through the lens holder onto the face of the blank 1, the face 2 of the blank is preferably treated with a coating of shellac or a relatively soft pitch, to insure the easy separation of the blank from the holder after the manufacturing operations have been finished. It also has the advantage of making the pitch flow better over the surface and gives a uniform contact between the pitch and the lens blank, and is commonly referred to as alens coating. The lens is cemented to the block in the axially aligned position described above so that the lens will be automatically seated in centered position on the grinding tool of the grinding machine.

The edge thicknesses of the blanks may be gauged by calipers through the recesses 14, Figure 5 and Figure 4. These recesses are cut back portions through the lip of the lens holder 10. Where spherical lenses are being operated upon it is only necessary to have two of these recesses diametrically arranged. lVhere toric or other irregular form lenses are used four or more recesses may be utilized.

It will be apparent from Figure 2 that when the ring 11 of the lens holder 10 is placed on the lens blank, the lens blank will be balanced and will automatically center itself on the raised portion 8 in those cases where the lens is of a toric or prismatic or unequal formation. The recesses 5, Figure 1-, and 9, Figure 2, are of sufficient depth to allow not only the thickness of the lens blank to be accommodated, but also the ring of the holder 10 so as to guide it down onto the lens blank with sufficient play for operation.

The lens holder 10 has a reduced ring 15 adapted to receive another flanged ring 16, Figures 7 and 9, which is secured to the holder 10 by means of set screws 17 or other means so that it becomes solidly united to the lens holder but removable therefrom.

The object of this ring is to provide a grinding attachment for the lens holder. This grinding attachment has a countersink 18 adapted to receive the lens pin of a lens grinding machine, giving a universal connection therewith. One preferred way of making this center connection for the lens pin is to insert a hardened block 19 in the central recess of the attachment 16 having the countersink recess 18 therein.

If desired in order to insure a positive locking of the pitch in the holder the tapered hole in the holder 10 may have re 'esses 21, Figure 9, or may be otherwise channeled, scored, or ribbed to give the proper engagement.

lVhen the holder 10 and the ring 16 have been secured together the blank is in shape to be applied to the grinding machine, see Figure 10. The grinding pin of the grinding machine is placed in the countersink 18, the glass blank being brought in contact with the lap 22 of the grinding machine for rough grinding, fine grinding, or polishing, as may be required. In the form shown the lap is revolved by a pulley 23 and belt 24, and the upper spindle by pulley 25 and belt 26, the grinding pin of the machine being an offset crank 27 on the upper spindle Q8. The grinding means shown in Figure 10 is only one of many machines that may be utilized for this purpose and simply shown by way of illustration to illustrate the adaptation of the lens holder to grinding machines.

It will be apparent from a study of the drawing and the description that the adhesive holding the lens to the lens holder in this process is localized, it being introduced through the opening in the lens holder and being entirely a 'ent from the prior art methods wherein pitch was placed over the face of the entire holder, especially where many lenses were held upon a block. It will. also be apparent that with this method of centering and securing the blank to the lens holder in centered position. that the abso lute centering is maintained throughout all the grinding and finishing operations, especially where the blank may be submitted successively to several different machines or processes.

The reason for tapering the walls of the hole 12 in the holder 10 is to provide a more rigid support for the central portion of the glass blank and also to give the widest area of pitch contact with the face of the glass blank.

Having described my invention, I claim:

1. The process of blocking a lens blank having a regular curved surface and a surface to be ground, comprising placing the surface to be ground in aligned position in contact with a contact seat on a support adapted to support the lens blank in the proper position during the blocking operation, and placing a hollow lens holder in contact with the opposite surface of the lens blank with a portion of the lens holder in interengagement with a portion of the support, thereby holding the lens holder in proper position with respect to the support and hence with respect to the lens which is positioned on the support, and injecting an adhesive into the lens holder so that the adhesive will adhere to the surface of the lens blank and to the inner walls of the lens holder and secure the lens blank to the lens holder.

2. The process of blocking a lens blank having a finished optical surface on one side and a surface to be ground axially with the surface on the first side, comprising placing the surface to be ground in aligned axial position with the first surface in contact with a contact seat on a support adapted to support the lens blank in the proper axial position during tie blocking operation and placing a lens holder in contact with an aligning surface that aligns the lens holder axially with the said first surface of the lens blank with a portion of said lens holder in interengagement with a portion of the support whereby the lens holder will be held in proper axial position with respect to the support and hence with respect to the lens which is positioned on the support and injecting an adhesive into the lens holder so that the adhesive will adhere to the surface of the lens blank and to the lens holder and secure the lens blank to said holder.

3. The process of blocking a lens blank having a finished surface and a surface to be finished to an axial relation with said finished surface to a lens holder, comprising placing the lens blank on a support with its surface to be finished in engagement with a contact seat on said support for locating the lens blank in predetermined relation to the support and to aligning means on said support, placing the lens holder in cooperative relation with the aligning means and lens blank with the axis of the holder coincident with a line radial with the center of the surface to be finished on the blank so that the holder will be supported in said relation and applying an adhesive to the lens blank and holder while in said relation so that the adhesive will adhere to the surface of the lens blank and the surface of the holder and secure the lens blank to said holder.

HARRY W. HILL. 

